Pantograph devices of trolley-type trucks are described in Japanese Patent Application Laid-Open No. 63-35102 (Patent Literature 1), Japanese Patent Application Laid-Open No. 2002-67776 (Patent Literature 2), and the like.
Patent Literature 1 describes a dump truck used for ore transportation at large-scale mines. According to the description, the dump truck travels by a generator driven by an engine in a non-trolley mode; and the dump truck collects a current from a double-track type overhead wire by a pair of pantographs mounted thereon and travels on utility power in a trolley mode. Patent Literature 1 also describes an invention for urgently causing the pantographs to descend when the pantographs are detached from an overhead wire.
Patent Literature 2 describes a trolley-type truck driven by driving drive motors on power from a current collector. This trolley-type truck is mounted with an engine generator that is started and can drive the drive motors when power supply from an overhead wire cannot be obtained. Patent Literature 2 also describes an invention in which a rocking arm (pantograph) is rocked and energized upward through a link arm and a coil spring to press a current collecting roller against an overhead wire; and when not in use, the rocking arm is pulled down by rewinding a rope coupled to the top end thereof on a hoisting winch.